Methods for processing agricultural grains, the term “grain” to include grains, legumes, seeds and other high-fiber plant components and plant by-products throughout and for the purposes of this application, particularly methods that consume and convert soluble dietary fiber and starches, and reject insoluble dietary fiber, are known. Whole kernels of grain include the following components: the hull, the germ, and the endosperm. Dietary fiber, both soluble and insoluble, is distributed across these various components of the grain kernel. For example, about half of the dietary fiber in corn is in the bran and hull portions of the whole corn.
Dietary fiber is typically separated and removed from the grain during grain processing. Dietary fiber is preferentially removed from the grain when fiber-containing components of the grain kernel are separated during the processing of the whole grain kernel. For example, dietary fiber tends to be concentrated in certain grain components such as the bran. Thus, during grain milling a substantial portion of the dietary fiber can be removed by separating out the bran portion of the grain after grinding.
Dietary fiber rejected with the bran, hulls, and so forth can be further processed in multistage manufacturing processes to produce useful products such as dietary fiber gels. Dietary fiber that is not rejected with the bran, hulls, and so forth stays with the non-bran and non-hull portion of the grain. During further processing to the grain, the remaining dietary fiber is typically rejected as a waste and is often used for animal feed.
Other grain processes feed the whole kernel of grain. Although some of the dietary fiber in grain kernel can be consumed or converted to other desirable products, most of the insoluble dietary fiber is rejected early in the grain process with rejected solids. For example, in the production of masa, corn flour used in the production of arepa, tortillas, chips and other related corn-based products, the whole kernels of corn are pre-cooked or steeped. Corn hulls and other solids that contain insoluble fiber are rejected during this initial masa production step of steeping. Similarly, in the processing of grain to produce alcohol for human consumption and gasohol production, starch is enzymatically depleted fro the whole grain kernel. The remaining solid residue, which contains insoluble dietary fiber, is rejected from the process. Generally, the solid residue is filtered off after the enzymatic hydrolysis of starch, and contains protein, lipids, and dietary fiber from all the various grain components such as the hull, the germ, and the endosperm. The depletion of dietary fiber from each of the various grain components can vary depending on the specifics of the grain and its processing.
The fiber-containing residue can be rejected as solids or slurry that contains solids depending on the grain process. In either situation, the solids typically contain soluble and insoluble fiber that potentially can be converted into higher valued products such as dietary fiber gel, adhesives, and so forth. Although the rejected solids from some grain processes can be recovered, typically, the recovered solids are used in relatively low economical value applications such as supplements to animal feeds. Alternatively, the rejected solids may not be suitable for human and animal consumption and must be disposed of in an environmentally safe and typically costly manner, i.e. the grain processor may have to pay to land fill the rejected solids. Although yielding higher valued products from the rejected solids, particularly from the associated insoluble dietary fiber, can improve grain processing economics, the recovery and conversion of rejected solids generally involves multiple complex processing steps and is uneconomical.
Accordingly there is a need for a simple process that can accept grain processing residue and by-products that contain dietary fiber from a variety of grain processes, yet can convert the contained dietary fiber into useful products such as insoluble amorphous cellulose in the form of fiber gel, aqueous products that contain soluble cellulose for use wood components, and so forth.